Closed loop solar collector system with dual reservoirs and fluid bypass

ABSTRACT

A closed loop solar collector system includes a linear concentrating parabolic reflector, a linear vaporizer tube horizontally aligned along the focal line of the parabolic reflector, and a fluid metering assembly attached to the input end of the vaporizer tube for precisely metering a quantity of a vaporizable heat transfer fluid from a supply tank to the vaporizer tube. Solar energy concentrated by the parabolic reflector on the vaporizer tube vaporizes the heat transfer fluid. The heated vapor flows out the outlet end of the tube opposite the fluid metering assembly through a pipe and enters a heat exchanger. The heat exchanger contains a heat absorptive medium which absorbs heat from the vaporized fluid to cause the fluid to condense and release its latent heat of vaporization to the heat absorptive medium. The condensed fluid flows back to the heat storage tank for re-use under pressure provided by the vaporized fluid entering the heat exchanger. A valve conduit is provided to cause the heat transfer fluid to bypass the heat exchanger and return to the fluid supply to maintain system fluid supply at a high level. A valved bypass around the fluid metering assembly is provided between the fluid supply and the vaporizer tube to supply sufficient heat transfer fluid to the vaporizer tube when pressure in the linear vaporizer tube exceeds a predetermined level. The fluid supply is provided with a two-chambered reservoir connected by a level controlled valve to assure the fluid in the system is maintained at an optimum temperature. A valved bypass responsive to the temperature of the heat transfer fluid measured in the vaporizer tube is provided between the fluid supply and the linear vaporizer tube. Accordingly, when the temperature of the heat transfer fluid drops below a predetermined level, the fluid in the supply empties into the vaporizer tube and the remainder of the closed loop system in order to minimize heat loss. A thermoelectric generating system using the present closed loop solar system is also provided utilizing a separate loop with a working fluid, such as ammonia, to drive an electric generator.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of pending application,CLOSED LOOP SOLAR COLLECTOR SYSTEM, Ser. No. 043,799 filed May 30, 1979,now U.S. Pat. No. 4,286,579, issued Sept. 1, 1981.

TECHNICAL FIELD

The invention here presented is broadly in the art of solar energycollectors. More specifically, it is concerned with a closed loop solarenergy collecting system and improvements devised to increase theefficiency of the operation of the system.

BACKGROUND ART

A closed loop solar energy collecting system has been described in mypending application mentioned above. The system includes a concentratingreflector, vaporizer means at the focal point of the reflector, a fluidmetering assembly attached to the input end of the vaporizer means forprecisely metering a quantity of a vaporizable heat transfer fluid froma supply tank to the vaporizer means, a heat exchanger, and a fluidstorage reservoir. Solar energy concentrated by the reflector on thevaporizer means vaporizes the heat transfer fluid. The heated vaporflows out the outlet end opposite the fluid metering assembly through apipe and enters a heat exchanger. The heat exchanger contains a heatabsorptive medium which absorbs heat from the vaporized fluid to causethe fluid to condense and release its latent heat of vaporization to theheat absorptive medium. The condensed fluid flows to the heat storagetank and back to the supply tank for reuse. The recirculation isprovided under pressure generated by the vaporized fluid entering theheat exchanger. The heat exchangers are modular and a plurality may beinterconnected to provide a desired amount of heat storage capacity.

During operation of such a system, several conditions may result whichdetract from the operating efficiency of the system. Since the pressureof the vaporized fluid moves the condensed heat transfer fluid from thestorage reservoir back to the fluid supply, conditions which dissipatethe pressure tend to reduce the rate of return of the condensed heattransfer fluid back to the fluid supply. One such condition is theoverall volume of the operating portions of the closed loop system. Attimes, a temporary reduction of the volume of the operating portions ofthe system is desired to lessen pressure dissipation in order to assureadequate return of condensed heat transfer fluid to the fluid supplytank.

Another condition which reduces the operating efficiency of the systemoccurs when extremely favorable sun conditions cause the linearvaporizer tube to heat up to a very high temperature. Concomitant withthe very high temperature is a high pressure. The excessive heatconditions may cause the linear vaporizer tube to overheat or rupture.

Another condition which contributes to overall inefficiency is heat lossthat results in the fluid supply tank. As hot fluid in the tank awaitsbeing metered into the linear vaporizer tube, it tends to lose some ofits heat to its surroundings.

Yet another condition which contributes to system inefficiency is thecooling and loss of heat from the heat transfer fluid to the outsidesurroundings of the system during conditions of low solar energy capturesuch as in the evening when the sun goes down or on cloudy days.

A thermoelectric generator system deriving its motive heat from solarenergy, should make most efficient use of the solar energy which iscollected and stored.

Therefore, it is an object of the invention to provide a closed loopsolar energy collector system of improved operating efficiency havingmeans to temporarily reduce the volume of the operating system in orderto enhance ability of the pressure of the vaporized heat transfer fluidto move condensed heat transfer liquid back to the fluid supply.

Another object of the invention is to provide a means to quench thelinear vaporizer tube when subject to excessively high operatingtemperatures and pressure.

Another object of the invention is to provide a fluid supply tankdesigned to reduce heat loss from the heat transfer fluid to thesurroundings.

Another object of the invention is to provide a means for transferring alarge portion of the heat transfer fluid away from the outsideenvironment to portions of the system which are protected from theoutside environment during low solar energy accumulating times such asafter sundown or on cloudy days.

Another object of the invention is to provide a combined solar energycollecting and electric energy generating system which makes efficientuse of the solar energy collected.

These and other objects are accomplished by the invention as describedbelow.

DISCLOSURE OF INVENTION

A basic closed loop solar energy collecting system having a fluid supplytank, a fluid metering system, a linear concentrating parabolicreflector, a linear vaporizer tube horizontally aligned along the focalline of the parabolic reflector, a heat exchanger, and a heat transferfluid storage reservoir is provided with improvements designed toincrease operating efficiency. Although the linear parabolic reflectorand the vaporizer tube have been shown and described as the preferredembodiment, it should be understood that other collectors may be used,such as a circular reflector and centrally located vaporizer bulb, oreven a flat plate-type collector.

In one improvement feature of the present invention, the heat transferfluid storage reservoir is divided into two separate reservoir portions.One portion is in direct communication with the linear vaporizer tubethereby bypassing the heat exchanger and the second portion of the fluidstorage reservoir. A valve, controlled by pressure of the condensedfluid in the fluid supply as sensed by a diaphragm-type pressure sensor,temporarily opens or closes communication between the linear vaporizertube and the heat exchanger and second reservoir portion therebytemporarily changing the operating volume of the system. Whencommunication to the heat exchanger and second portion of the fluidreservoir is cut off, the operating volume of the system is decreased.

In a second improvement, a pressure-controlled valve is provided toenable bypassing the fluid metering assembly and permit directcommunication between the fluid supply tank and the linear vaporizertube. This will allow quenching of the linear vaporizer tube underconditions of excessive temperature and pressure buildup.

In a third improvement, the fluid supply tank is partitioned into twofluid supply chambers having a valved orifice connecting the twochambers. The valve is dependent upon the level of heat transfer fluidin the first chamber. When the level of the heat transfer fluid is highenough in the first chamber, the valve connecting the two chambers isclosed. The heat transfer fluid contained in the second chamber issequestered from the operating system. The heat transfer fluid in thefirst chamber circulates through the operating system rapidly. Itsresidence time in the first chamber is relatively short therebylessening heat loss from the heat transfer fluid to the surroundings.When the level of heat transfer fluid in the first chamber drops, thevalve between the two chambers opens thereby allowing the contents ofthe second chamber to enter the operating system.

In a fourth improvement, a temperature-responsive valve is connectedbetween the fluid supply tank and the linear vaporizer tube and servesto bypass the fluid metering assembly. When the temperature of the heattransfer fluid sensed in the linear vaporizer tube falls below apredetermined level such as after sundown or on a cloudy day, thetemperature-responsive valve opens and allows the heat transfer fluidcontained in the fluid supply tank to drain into the linear vaporizertube and the remainder of the system enclosed by the building structure,such as a house, thereby serving to retain the heat collected by theheat transfer fluid and to reduce the amount of heat that would be lostfrom the system to its outside surroundings.

In a fifth improvement, a thermoelectric generating system employing theclosed loop solar energy collector system as its source of heat energyis provided with a fluid circulation system which is in heat exchangecommunication with the heat exchanger of the collector system. Thereby,the working fluid of the thermoelectric generating system, for exampleammonia, is heated by the heat stored in the solar collector system.

The novel features characteristic of the various aspects of theinvention as to their organization and method of operation, will best beunderstood by the description presented below when read in connectionwith the accompanying drawings. Although the description presented belowrelates especially to the embodiments of the invention illustrated inthe drawings, this description is not intended to limit the scope of theinvention which is defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the overall solar collector system.

FIG. 2 shows an embodiment of the invention having a two-part fluidstorage reservoir. The system is in the operating mode.

FIG. 3 shows a pressure-controlled valve designed to allow bypass of thefluid metering assembly.

FIG. 4 shows a fluid supply tank having two partitioned supply chambers.

FIG. 5 shows an embodiment of the invention having atemperature-responsive valve which opens and drains the fluid supplytank to the remainder of the system. The system is shown in the shutdown mode.

FIG. 6 is a schematic diagram of the thermoelectric generating system ofthe invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 showing a perspective view of the overall solarcollector system, linear concentrating parabolic reflector 1concentrates captured solar energy onto linear, fluid receivingvaporizer tube 3 which is disposed along the focal line of thereflector. Fluid supply tank 11 is connected to the linear vaporizertube 3 by hose 9. Pressure equalizing hose 13 runs from tank 11 toreceiver 3, also. Fluid metering valve 37 is attached to the linearreceiver 3 and precisely meters heat transfer fluid from the fluidsupply tank 11 to the linear receiver 3. The outlet end of the receiver3 is connected to heat exchanger 17 by means of conduit 15 and pipe 16.

In heat exchanger 17, heat exchanger channels or manifolds 23 allowtransfer of heat from the heat transfer fluid to heat absorptive medium25 inside the heat exchanger 17. A number of secondary fluid transferchannels 28 are disposed within heat absorptive medium 25 and allow aflow of heat extraction fluid, such as air, therethrough as shown byarrows A. The heat extraction fluid absorbs heat from the absorptivemedium of the heat exchanger. The secondary heat extraction fluid canalso be water or another fluid and used, for example, to heat a home oroffice building, heat water, operate the vaporization cycle of air airconditioning unit, or power a thermoelectric generator.

Of course, many other uses of the heat extracted and stored by medium 25will occur to those skilled in the art. The heat exchange mediums can bea wide variety of known materials.

Condensed heat transfer fluid flows from heat exchange channels 23 andenters heat transfer fluid reservoir 27. Condensed heat transfer fluidfrom reservoir 27 is forced upwardly in the system under pressuregenerated in the vaporizer tube 3 through pipe 29 and into fluid supplytank 11. A one-way gate or check valve 31 is disposed in pipe 29 toprevent backflow of fluid from tank 11. The fluid in tank 11 is readyfor reuse in the closed loop solar collector system.

The heat from the closed loop solar collector system described above,can be used, for example, to heat air or water for domestic space or hotwater heating systems, to power the vaporization cycle of an airconditioning unit, or to power a thermoelectric generator. It is thisbasic system that forms the foundation for the improvement features ofthe present invention, as will now be described.

The first improvement feature or aspect of the solar collector system ofthe present invention, is shown in FIG. 2. Valve means 113 is disposedwithin pipe 16 which is connected to the linear vaporizer tube 3 and tothe heat exchange channels 23. The valve 113 is controlled by apressure-differential sensing means 125 which is comprised of chamber118, diaphragm 119, and adjustment screw 120. The valve 113 operates inresponse to the pressure difference between the vaporized heat transferfluid from valve 113 exerted on the topside of diaphragm 119 and thecondensed heat transfer fluid, transmitted through pipe 201, on thebottomside of diaphragm 119. When the pressure of the condensed fluid isless than a predetermined level, the amount of fluid in fluid supplytank 11 is low. When this condition is sensed, valve 113 closes, thusterminating fluid flow to the heat exchange channels 23 and the firstheat transfer fluid reservoir 51 connected thereto. Because of thetemporary reduction of the volume of the operating system, the pressureof the vaporized fluid has greater effect in circulating the condensedheat transfer fluid through the system.

A second heat transfer fluid reservoir 52 is connected between the fluidsupply tank 11 and the linear vaporizer tube 3. It is additionallyconnected to the first heat transfer fluid storage reservoir 51 withone-way gate or check valve 117 disposed between the two fluid storagereservoirs. When valve 113 shuts off heat exchange channels 23 and firstfluid storage reservoir 51, the pressure of the vaporized heat transferfluid acts directly upon the condensed heat transfer fluid 115 stored inreservoir 52 to move it into fluid supply tank 11. As the level ofcondensed fluid builds up in tank 11, the pressure of the condensedfluid on the bottomside of diaphragm 119 of pressure sensor 25increases. At a predetermined pressure differential, valve 113 opensreopening heat exchanger channels 23 and fluid reservoir 51 to theoperating system.

In FIG. 3, a pressure-controlled valve 121 allows bypass of fluidmetering assembly 37 when excessive pressure and temperature conditionsdevelop in linear receiver tube 3, such as when solar energy inputconditions are very favorable. Valve 121 is actuated by pressuredifferential sensing diaphragm 122. Pressure exerted by the vaporizedheat transfer fluid is exerted on the bottomside of diaphragm 122.Pressure exerted by weight 191 is exerted on the topside of diaphragm122. At a predetermined pressure differential, valve 121 is actuatedallowing condensed heat transfer fluid to flow from supply tank 11 (seeFIG. 1), through conduit 9, through valve 121, through pipe 192, andinto receiver 3, thereby bypassing fluid metering assembly 37. Uponreceiving condensed heat transfer fluid from supply tank 11 at a rapidrate, the excessive pressure and temperature conditions in receiver tube3 are quenched.

Rod 124 is attached to the valve stem and diaphragm 122 and serves toopen valve 65 which is disposed between pressure equalizing hose 13 andreceiver 3. Particularly, rod 124 is connected to pivotal lever arm 123which forces plunger blocker 126 of the plunger 61 down, opening valve65 when diaphragm 122 moves upward as a result of high pressure inreceiver 3.

In FIG. 4, fluid supply tank 11 is partitioned into a first supplychamber 129 and a second supply chamber 130. Valve 133 is responsive tothe level of condensed heat transfer fluid in first supply chamber 129.When the level of the fluid in chamber 129 is sufficient, float 131 isbuoyed up by the fluid. However, when the level of fluid lowerssufficiently, float 131 is no longer buoyed up; it then rests onspring-biased rod 138, thereby opening valve 133 and allowingcommunication between first supply chamber 129 and second supply chanber130. Float 131 may be connected by rod 139 to valve 132 which controlsflow of condensed heat transfer fluid from second supply chamber 130 toconduit 9 connecting the fluid supply tank 11 to the fluid meteringassembly 37 (see FIG. 1).

When first supply chamber 129 is emptied, float-controlled breathervalve 103 is opened; valve 133 is opened; and valve 132 is opened. Fluidmay then flow from second supply chamber 130 into conduit 9 without avacuum being created in chambers 129 and 130 due to displaced fluid.Atmospheric air enters chambers 129 and 130 through valves 103 and 133,respectively. When fluid returns to the fluid supply tank 11 insufficient quantity, second supply chanber 130 fills up first, followedby first supply chamber 129.

In most operating circumstances, first supply chamber 129 has sufficientcondensed heat transfer fluid to preclude the fluid in second supplychamber 130 from entering the operating system. This is desireablebecause the smaller amount of fluid in first chamber 129 circulatesthrough the operating system in considerably less time than would thelarger amount of fluid retained in second chamber 130. By having areduced residence time in first supply chamber 129, the hot, condensedheat transfer fluid entering first supply chamber 129 undergoes lessheat loss to the surroundings of the fluid supply tank. Less heat lossto the surroundings increases the efficiency of the operating system.The partition 140 between the first and second supply chambers may beprovided with insulation 134 to further reduce heat loss.

In FIG. 5, valve 135 controls flow through conduit 136 which serves toconnect fluid supply tank 11 with linear vaporizer tube 3, therebybypassing fluid metering assembly 37. Valve 135 is controlled by astandard temperature-responsive control means 198 connected by tube 137to temperature sensor 138. Under normal operating circumstances, thetemperature of the heat transfer fluid in linear vaporizer tube 3 whichis sensed by sensor 138 is sufficiently high so as to keep valve 135closed. However, during times of decreased solar energy input, such asduring cloudy days or after sundown, valve 135 is opened as a result ofthe lower threshold temperature being sensed by sensor 138. When valve135 opens, heat transfer fluid drains from fluid supply tank 11 to thelinear vaporizer tube 3 and to the rest of the system including heatexchange channels 23 and condensed fluid storage reservoirs 51 and 52.Fluid level 200 approximates the level of the heat transfer fluid aftervalve 135 opens and the heat transfer fluid is dumped from tank 11.

The overall solar collector system is designed so that only a minimalportion of the system is placed outside the confines of the building 139or other structure that the system services. By shifting as much heattransfer fluid to the building as is possible during times when solarenergy input to the system is low, heat loss from the heat transferfluid to the outside surroundings is kept to a minimum.

For a combined solar energy collecting and electric generating system, aclosed loop solar collecting system such as described above and shown inthe drawings, may be employed in conjunction with an electric generatingsystem which includes a working-fluid-powered turbine/generator 202 (seeFIG. 6). The working fluid is preferably ammonia, which is in heatexchange communication with the heat exchanger 17 by passing throughchannels 28 (FIG. 1) of the solar collecting system. The heat exchangedfrom the heat exchanger 17 generates the working vaporized, highenthalpy fluid which drives the turbine/generator 202. A condenser/sumpand a return pump 205 may be provided to complete this secondary orworking electric generating system (FIG. 6).

In view of the foregoing, it is readily apparent that the closed loopsolar collector system of the present invention, is a significantimprovement over the basic system. Dual reservoirs 51, 52 and a bypassvalve 113 effectively limit the operating volume of the system to assureproper operating pressure for return of fluid to the supply tank 11.Secondly, the bypass valve 121 assures a rapid quench of the vaporizertube 3 when overly favorable solar conditions tend to over-heat thesystem. On the other hand, during times of low heat input the valve 135opens to bypass metering valve 37 thereby removing the fluid from supplytank 11 and connecting lines to minimize heat loss.

A fluid supply tank 11 having dual supply chambers 129, 130 assuressufficient quantity of fluid at all times while limiting the volumeduring normal operation to also minimize lost heat. Finally, anelectrogenerating system is provided utilizing the features of theinvention.

In this disclosure, there is shown and described only the preferredembodiments of the invention, but as aforementioned, it is to beunderstood that the invention is capable of use in various othercombinations and environments and is capable of changes or modificationswithin the scope of the inventive concept as expressed herein.

I claim:
 1. A closed loop solar collecting system, comprising:a fluidreceiver for collecting solar heat; fluid supply means, connected tosaid fluid receiver, for supplying a quantity of vaporizable heattransfer fluid to said fluid receiver; means attached to said receiverfor precisely metering a quantity of heat transfer fluid from saidsupply means; valve means connected to said fluid supply means and tosaid fluid receiver for bypassing said metering means and supplying saidfluid receiver with heat transfer fluid from said fluid supply meanswhen the pressure inside said fluid receiver reaches a predeterminedlevel; heat exchanger means connected to said fluid receiver forabsorbing heat energy from the heat transfer fluid which is vaporized insaid receiver, the vaporized heat transfer fluid condensing afterreleasing its latent heat of vaporization to said heat exchanger, thecondensed fluid flowing under pressure provided by the vaporized fluidentering said heat exchanger means to said supply means.
 2. A closedloop solar collecting system as described in claim 1 further including apressure equalizing means having valve means connected between saidfluid supply means and said fluid receiver;wherein said valve meansincludes a pressure sensing means for sensing the pressure within saidfluid receiver; and wherein said pressure sensing means includes meansfor operating said valve means of said pressure equalizing means forequalizing the pressure between said fluid supply means and said fluidreceiver.